Process for production of sulphur dioxide



May 2, 1939. A. c. MOHR PRocEss Fon PRODUCTION oF suLPHUR 1110x1111 yFiled July e, 1937 l ATTORN Patented May 2, 1939 UNITED lSTATES PROCESSFOR PRODUCTION OF SULPHUR DIOXIDE Albert C. Mohr, Berkeley, Calif.,assignor to Stauffer Chemical Company, a corporation of CaliforniaApplication July 6, 1937, Serial No. 152,082

2 Claims.

This invention relates to the production of sulphur dioxide. Thismaterial has an extensive commercial use. In the presence of moisture itcombines to form sulphurous acid which is corrosive to many materials.Consequently, in the use of sulphur dioxide it is a requisite that thesulphur dioxide be dry so that thereafter it can be used successfully inthis state and corrosion avoided. The dryness required is of the orderof less than fty parts of water per million and commercial sulphurdioxide is commonly supplied to the trade at less than twenty parts permillion.

The present manufacturing operations for the production of anhydroussulphur dioxide include rectication which removes the water from thesulphur dioxide by fractional distillation. The `sulphur dioxide isproduced by the direct combustion of sulphur with substantiallyanhydrous air. I have found that it is not necessary to utilize thisprocess and that sulphur dioxide can be produced directly from sulphurutilizing sulphur trioxide as the oxidizing agent. By utilizing sulphurtrioxide, drying of the air is unnecessary. Since it is relativelydiilicult to get the air absolutely dry, this use of sulphur trioxideavoids possible contamination of the nal product.

It is generally the broad object of this invention to provide a novelprocess for the production of sulphur dioxide.

Another object of the invention is to provide a process for the directproduction of substantially pure anhydrous sulphur dioxide.

The process will become further apparent upon considering the following,wherein the present preferred manner of practicing the process of thepresent invention is disclosed. The drawing is a diagrammaticillustration of the manner of practicing the invention.

I und that if sulphur is rst melted in a vessel 8 heated as by steamcoil 9 to above its melting point, and if substantially dry air is thenblown through the sulphur, the molten sulphur, when passed through thesulphur vaporizer Ii, will provide substantially dry, water-free sulphurvapor. It has heretofore been proposed to maintain the sulphur at itsmelting point for a considerable length of time. However, it has beendetermined that this is not sufficient to drive off the moisture presentin the sulphur, suflicient moisture being retained by the molten sulphurto make the SO2 so wet that rectification of the S02 is a requisite.

From the sulphur vaporizer Il vaporized sulphur maintained at atemperature above that at which sulphur begins to condense, is passedinto a reactor I4. In this reactor the vaporized sulphur is reacted withsulphur trioxide supplied through line I6: S+S03 2S02- The sulphurtrioxide is conveniently generated by heating oleum, or fuming sulphuricacid containing excess sulphur trioxide (10o-110% H2S04). The gases,sulphur and sulphur trioxide, are passed through the reactor whereinthey are suitably contacted, the reactor being maintained at a pressureabove the dew point of sulphur from the gases. The oleum can be suppliedthrough line Il into a still I3. In this still, sulphur trioxide isboiled oil into line I6; while the H2S04 is conveniently removed throughline t9. Any other source of S03 can be used as the output of a Contactsulphuric acid plant, the S03 being taken off before the absorber.

Line 2| conveys the sulphur dioxide away from the reactor. Dependingupon the use to which it is to be put, it may or may not be scrubbedwith a dilute sulphuric acid (98%) to remove any traces of S03. The dry,pure S02 is removed from column 22 in which it is scrubbed withsulphuric acid supplied from line 23. The sulphur dioxide, in pure dryform, is removed from the top of the column through line 24, while theacid is removed at the base of the column through line 26. The sulphuricacid in column 22 can be removed to a still 21 to distill off the SO2.

It is not entirely practical to operate the process with thestoichiometric volumes indicated and I therefore prefer to operate witha slight excess of sulphur trioxide. This excess can vary up to 20%. Theuse of this excess has the advantage of removing any water present assulphuric acid. Since the gases are subsequently scrubbed with acid inwhich S03 dissolves, practically dry pure S02 is readily available on acommercial basis.

The reaction of sulphur vapor and sulphur trioxide is exothermic and thegas in line 2| will therefore be quite hot. This heat can be usedadvantageously by diverting the hot gas containing an excess oftrioxide, through line 3| into blower 32, This device discharges intoline 33 connected to distribution plate 34 in the sulphur vaporizer. Thehot gas vaporizes sulphur when the sulphur in vaporizer H is above itsmelting point. This vapor reacts with the Sm in the vaporizer tovaporize more sulphur. The mixture of SO2 and sulphur vapor passes onthe reactor wherein excess S03 is added to free the gas of the sulphurvapor and form SO2.

2. A process for production of SO2 comprising vaporizing S with hot S03gas to oxidize the S to SO2 and form sulphur vapor and then oxidizingthe so formed sulphur vapor with S03 gas to form a hot gas mixture ofSO2 and S03 and returning at least a. portion of the hot gas mixture asthe hot S03 gas to vaporize S.

ALBERT C. MOI-1R.

